Group 1: Doesn't like Steam.
Some had problems with it
Some object to being hassled when playing the game (i.e. it really wants the player to be connected to the net when the game is started).
Some object to having an extra client running in order to play a game.
Myself, I don't belong to this group. I like Steam. I have never had any problems with it except when it first came out. Steam got a big head start because of Valve's own games but I can tell you that it is the market leader because it has earned it.
Group 2: Doesn't like Steamworks.
They fear (based on other games that have used Steamworks) that it will cripple modding.
They don't like that it requires the Steam client to access its features.
I have concerns over this but I tend to see this as a developer issue than a problem of Steamworks. SecuROM has an undeserved bad reputation because some publishers made use of draconian features they make available. Steam and Steamworks can certainly lock down a title so that all players have to have the same CRC but it doesn't have to be that way. This is an issue that people, I think, should wait and see on.
So I don't belong to group 2 either.
Group 3: Doesn't want PC gaming to become a closed platform.
Object to major publishers locking the purchasing options of a title to a platform that already has 70% of the digital market share.
Object to "special editions" of third party titles being made available exclusively on the platform with 70% of the digital market share (i.e. Civilization Deluxe).
Know how other closed platforms work already - what is released and how it's released is determined by the platform owner (no Google Voice on the iPhone, tons of Xbox 360, Wii, and PS3 titles never see the light of day).
Can easily envision a day where all titles require Steamworks (using achievements and such) to be sold on Steam, updates cost the publisher money to go through certification and thus DLC becomes non-free for certain (this was the GFWL original concept btw).
I wonder where I fit. I like the Steam service itself; I bought the Orange Box at retail and played Team Fortress 2 quite a bit, and found the matchmaking, updating, and achievements systems to be excellent. The community features are probably very nice as well, but I don't know because I don't have any friends there.
However, Steam brings with it a bunch of DRM baggage that I simply find unacceptable. I can understand the client needing to load and authenticate games for updates and online multiplayer, or loading at start for a multiplayer-only game like TF2, because the client is providing the backend for those things and I usually have to be online for them anyway. What bothers me is having to load the client and authenticate for singleplayer. It makes the game take longer to start up, and prevents me from playing offline. (I have a pretty good connection, but while it's never gone out during a thunderstorm, it has been taken down by high winds and occasional ISP incompetence. Also, what if I want to play on a laptop away from home?)
There's also the issue of Valve being able to confiscate my purchased games any time they wish. What if the authentication check goes wonky and won't let me play? What if someone hacks into my account and steals it or gets it banned? What if someone at Valve has a bad day and accidentally/deliberately breaks something or abuses the banhammer? What if a third-party licensing issue forces Valve to disable access to certain games?
This isn't just an academic issue or the paranoid ravings of a lunatic; Amazon did something very similar last year to Kindle owners when there was a dispute between publishers.
Google lists many accounts of people having their Steam accounts stolen, and while I don't think I would fall for the kind of scam involved, I'm not so naive as to say I'll never fall for any scam.
Guild Wars also recently had a lot of issues with hackers stealing accounts, with methods ranging from fansite data breaches to brute-force password hacks necessitating the addition of more security features. Losing one game account is bad enough; imagine having it happen to a Steam account with hundreds of dollars worth of games tied to it. Is Steam's account security better than Guild Wars' was? I have no way of knowing. What I do know is that if my Impulse account ever gets hacked, I can still access my installed games while I work with support to get it resolved.
Valve has also used Steam to remove unlocks and achievements from misbehaving players, but while most such acts are well deserved, the TF2 Hatpocalypse showed that they're perfectly willing to punish players ex post facto. If you can get items taken away for doing something not explicitly forbidden and which they've never said was wrong, then it's not hard to imagine losing your entire account for some accidental infraction. I don't have to worry about this as much with Impulse, because Stardock can't take away games I've already downloaded and installed. I don't need their permission to play.
The bottom line is that, in my opinion, Steam is not a safe place to buy games. I simply can't justify spending $50-$60 on a product that can be taken away from me on a publisher's whim.
As for group 3, I know the dangers of a closed software ecosystem and don't like title exclusivity, but I see the PC as an inherently open platform. Steam may have or gain market dominance, but developers always have the option of making their own services and selling games online the old-fashioned way: from their websites. The fact that Impulse and so many other digital distribution services exist is proof of this. Now, if Steam suddenly starts requiring exclusivity for all titles, that could be a problem due to their large number of users and the fact that small developers of multiplayer-centric games don't have many options if they can't afford to host their own matchmaking service. In that case, I'd expect some rapid consolidation as the other services try to combine their userbases. As for the multiplayer backend, I think that's where this Reactor thing comes in. It's starting to seem really important that Stardock gets it out there as soon as possible, and I'm sure Frogboy's working hard to do just that.
So...
Group 4: Doesn't want to pay full price for an unspecified-term rental?